Fig. 1. pks+ E. coli synthesize cyclopropane-containing metabolites that may alkylate DNA.

(A) pks genomic island. Open reading frames encoding nonribosomal peptide synthetase (NRPS) (purple), polyketide synthase (PKS) (brown), hybrid NRPS/PKS (blue), peptidase (ClbP) (green), aminomalonate synthesis and transfer (grey), and other (black) enzymes are highlighted. (B) Selected cyclopropane-containing candidate precolibactins isolated and structurally characterized from pks+ ΔclbP E. coli, including lactam, pyridone, and macrocyclic scaffolds. (C) Illudin S and (+)-duocarmycin A are DNA alkylating metabolites that contain a cyclopropane ring.